In the recovery of downhole hydrocarbons, it is useful to inject fluids or fluid slurries into through the wellbore and to the hydrocarbon bearing formation to fracture or otherwise treat the wellbore or the hydrocarbon bearing formation. Typically, accessing a hydrocarbon bearing formation begins with drilling a wellbore through at least one hydrocarbon bearing zone. After the well is drilled the well is completed by inserting a casing into the wellbore, cementing the casing in the wellbore, and opening ports in the casing through which fluids may be injected into or removed from the formation. Although in some cases the casing is not cemented into the wellbore. In such a case packers may be used for zone isolation.
It may be desirable that a zone of a wellbore adjacent to a targeted hydrocarbon bearing formation be isolated from other zones of the wellbore. For example, if such a targeted zone is not isolated, the fracturing fluid that is pumped down the wellbore, will flow through the ports and then will travel along the exterior of the casing out of the targeted zone into areas that are not hydrocarbon bearing formations and perhaps even into other separate hydrocarbon bearing formations quickly overcoming the ability of the casing to transport the fluid into the formations and the ability of the pumps to supply the fluid at pressure sufficient to fracture the formation. Similarly, annular fluid flow between the wellbore and casing may result in reduced recovery of fluids, loss of treatment fluids, or infiltration of undesired materials into a targeted or untargeted zones.
Usually after a zone has been isolated, ports in the casing may be opened to allow for the injection of fluids or slurries into as well as the removal of fluids or slurries from the hydrocarbon bearing formation. It may be desirable that the ports may be selectively opened or closed. Typically the ports are installed in the well in a closed condition by use of sliding sleeves Typical sliding sleeve valves comprise a sleeve having circumferential seals such as O-rings at the top and bottom edges thereof to seal against a wall of the casing. Thus, when the sleeve is positioned over a port, the sleeve substantially prevents fluid communication between the interior of the casing and the hydrocarbon bearing formation through the port. The port may be opened by moving the sliding sleeve so that the sliding sleeve is located above or below the port or at least aligning a port in the sliding sleeve with the port in the casing thereby allowing fluid flow into or out of the desired zone.
More specifically, a tubular assembly is put together on the rig floor prior to being lowered into the well bore. If the operator does not plan to cement the tubular assembly into the wellbore annular zonal isolation packers will also be installed along the length of the tubular assembly. Typically a packer will be installed both above and below each port and spaced far enough apart to straddle a particular hydrocarbon bearing formation or at least a particular zone of a hydrocarbon bearing formation. In many instances a single packer may serve as the upper packer on one zone as well as the lower packer on an adjacent zone.
The tubular assembly is then lowered into the wellbore so that a port is adjacent to the desired zone, preferably hydrocarbon bearing formation with packers both above and below the zone to straddle the zone.
With the tubular assembly in place the operator then runs an internal packer or plug into the tubular assembly using a second tubular assembly, typically coil tubing. The operator will then land the plug below the lowest port. The plug is then set and the operator disconnects the coil tubing from the plug. Once disconnected from the plug the coil tubing connector is moved up the wellbore and is located adjacent the lowest sliding sleeve where the coil tubing connector latches into the sliding sleeve. The sliding sleeve is then moved from its closed position to its open position. Fluid, typically a hydraulic fracturing slurry, is pumped down the tubular assembly with the tubular assembly plugged below and all of the other sliding sleeves closed the fluid is forced out of the open sliding sleeve port and into the isolated zone. Once the treatment is complete the pumps at the surface are turned off, the operator disconnects the coil tubing connector from the sliding sleeve and lowers the coil tubing and the coil tubing connector to the packer. The packer is then unset and raised until it is above the lowest port and sliding sleeve but below the next higher port and sliding sleeve. The packer is then reset and the process of treating the well is repeated until each zone has been treated. Unfortunately, when a sliding sleeve is opened or closed the seals between the sleeve in the casing are damaged so that thereafter when the sliding sleeve is closed it will leak. Because the sliding sleeves leak when closed after being opened the operator can no longer rely on sliding sleeves to seal for in the event that the operator desired to treat or otherwise service a particular zone.